Simplicity

But what is the very best bridge structure, say from the point of view of robustness? There’s a huge universe of possibilities. But so far, only a tiny corner has been explored–and that mostly in the 1800s.

It’s very much the same as in other areas of engineering. People have come up with particular structures to consider. Most often they’re just based on a sequence of identical repeating elements, or sometimes of nested elements.